Just to add to all the possibilities, there could be an arc at the
balun. Most authorities suggest a 1:1 balun with a setup like this. As
you know, the impedance seen at the balun will vary all over the map,
depending on the band and the length of the 600-ohm line.
I've calculated that the voltage that appears at that point in my
somewhat similar setup is as high as 7 kV when I'm running 1200 watts on
one particular band. A 1:1 balun designed for tuner use (e.g., one like
this:
<https://www.dxengineering.com/parts/dxe-bal050h10at> or this:
<https://www.dxengineering.com/parts/dxe-bal050h11ct>
would be suitable.
73,
Victor, 4X6GP
Rehovot, Israel
Formerly K2VCO
http://www.qsl.net/k2vco/
On 24 Feb 2018 07:42, Chris Hallinan wrote:
Greetings from southwest Florida.
My KPA500 is kicking out with REFL HI warning (high SWR). But here is the
strangeness. My setup is K3->KPA500->40' coax->MFJ 600W remote tuner -> 4:1
balun -> open wire feedline to 80-meter doublet. In words, I have a remote
autotuner feeding an 80-meter doublet fed with 600-ohm open wire line. A
Balun Designs 4:1 balun provides the interface from the open wire line to
the tuner.
With the autotuner tuned at low power, the SWR shows 1.5:1 on my KPA500 and
external SWR meter. As I run the power up to 300, 400, 500 watts,
somewhere in there all of a sudden the SWR instantly jumps off the scale,
into the red LEDs on KPA500, and it faults. It's as if the SWR were
dependent on power.
Even stranger, when I back the power off to say 250 Watts, holding key down
the SWR is stable in the green (<1.5:1), but when I key it at CW rates, the
SWR bounces into the red on every dit and eventually faults, when at steady
state key down it never leaves the green zone!
I fear it is the tuner falling over, but it should be able to handle the
power. I see this on all bands from 80-20.
Operating into my 20-meter resonant vertical, with no tuner, everything
works fine.
Any ideas or hints on how to correct this?
Thanks,
Chris
73 de K1AY
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